Figure  Details of Earth's
energy balance (source: Kiehl
and Trenberth, 1997). Numbers are in watts per square meter of
Earth's surface, and some may be uncertain by as much as 20%. The greenhouse
effect is associated with the absorption and reradiation of energy by atmospheric
greenhouse gases and particles, resulting in a downward flux of infrared radiation
from the atmosphere to the surface (back radiation) and therefore in a higher
surface temperature. Note that the total rate at which energy leaves Earth
(107 W/m2 of reflected sunlight plus 235 W/m2
of infrared [long-wave] radiation) is equal to the 342 W/m2
of incident sunlight. Thus Earth is in approximate energy balance in this
analysis.